Injection molding has been well known and widely used in constructing relatively complex plastic parts, including those having empty space or spaces inside. Examples include plastic bodies of various tools, instruments, medical equipment, and personal-care implements, such as, e.g., various toothbrushes, both manual and power, the latter commonly housing power source and drive mechanism inside a hollow plastic housing, typically comprising the toothbrush's handle. These articles may comprise multi-component plastic bodies that include two or more plastic materials: a first material forming a hollow body and a second material that is at least partially molded over the first material. With respect to both manual and power toothbrushes, it may be desirable to create a hollow plastic body comprising two or more plastic materials such that a hollow component comprising a first plastic material is overmolded, at least partially, by a second plastic material.
It is generally known to use a gas-assisted injection molding process to create hollow articles. See, e.g., U.S. Pat. No. 6,645,587. In a gas-assisted process, a hollow body, comprising a first plastic material, typically includes an opening, or vent, through which the gas can enter, and escape from, the hollow body being created. Other injection molding processes, both involving gas and not involving gas, may also technologically require a vent or vents in the hollow body being created. For example, in a liquid-assisted injection molding, where gas is commonly used to purge the liquid following the liquid-injection step, typically at least two vents may be needed, one for liquid and the other for gas.
It is also known, e.g., that in an injection-molded component formed by using a customary mold tool typically comprising two mold parts (or “halves”) and a core, an opening or recesses used to create a hollow component can be formed by providing a slider or a pin retractable into one of the mold parts or the core. In such a configuration, a hollow component, comprising a first plastic material, can be created by using an opening unobstructed by the retractable pin. Then, the retractable pin can be moved in a position to close the opening, and a second plastic material can be applied to overmold the first-material component. Because the opening is closed by the pin, the second material is precluded from penetrating into the hollow component through the opening—as long as the pin is in place. But such a retractable pin, if removed before solidification of the second material, would not prevent the second material from leaking into the hollow component. And the removal of the retractable pin after solidification of the second material would result in the article still having the opening.
There is a need, therefore, to seal the opening, or vent, in the hollow body to eliminate, or at least significantly reduce, the risk of the subsequent, overmolding material penetrating through the opening into the void of the hollow body while the second material is being molded over a portion of the hollow body. The present disclosure is directed to a process and equipment for manufacturing a hollow article by injection molding, wherein some of the deficiencies of the commonly known methods, described above, are minimized. The present disclosure is also directed to a hollow article, such as, e.g., a plastic body of a toothbrush, comprising a hollow structure including a shell made from a first material overmolded by at least a second material.